Odontoid fracture with missed diagnosis of Transverse Atlantal Ligament (TAL) injury resulting in late-onset instability.

BACKGROUND: Concurrent injuries to both the odontoid and transverse atlantal ligament are rare and can be easily missed. Failure to diagnose both lesions potentially leads to the late onset of sagittal plane instability and acute myelopathy. Here, we present a patient with an odontoid fracture whose transverse atlantal ligament (TAL) injury was originally missed on magnetic resonance imaging (MRI) and computed tomography (CT) scans. He later developed atlantoaxial instability requiring surgery. CASE DESCRIPTION: A 17-year-old male presented with neck pain, restricted cervical range of motion, but a normal neurological exam following a motor vehicle accident. The original X-rays showed a moderately displaced type-3 odontoid fracture. Additional MRI and CT scans excluded ligamentous injury, and he was initially treated with 13 weeks of halo vest immobilization. Radiographs 5 months later showed an enlarged atlanto-dens interval (e.g., >3 mm); the diagnosis of an odontoid fracture with an accompanying TAL injury was established, following which the patient successfully underwent a posterior C1-C2 fusion.
CONCLUSION: Odontoid fractures require strict clinical and radiographic (X-ray, MRI, CT) surveillance to help rule out accompanying TAL injuries that may warrant surgical intervention.

INTRODUCTION

C2 fractures account for 20% of all cervical spine injuries, while odontoid fractures comprise 50% of these injuries.[2] Simultaneous injuries to both the transverse ligament and odontoid process are rare.[37] Injuries to the TAL are usually isolated or can be associated with atlas fractures. Early recognition of combined odontoid fractures and TAL injuries is critical to avoid delayed deformity and neurological injury. Here, we present a patient with both an odontoid fracture and TAL injury that was missed on the original MRI and CT studies. When he developed late onset of atlantoaxial instability, a C1–C2 fusion was warranted.

CASE REPORT

A 17-year-old male presented 4 days following a motor vehicle accident with neck pain, restricted range of motion, but neurologically intact. X-rays revealed a moderately displaced Anderson & D’ Alonzo type-3 odontoid fracture; however, the atlanto-dens interval (ADI) was maintained (e.g., excluding sagittal atlantoaxial instability) [Figure 1a]. Magnetic resonance imaging (MRI) ruled out a ligamentous injury [Figure 1b and c]. On computed tomography (CT), the ADI was less than 3 mm, and the fracture line was oriented from the posterosuperior margin of the odontoid base to the anteroinferior of the body of the axis [Figure 2]. There was no evidence of a transverse ligament injury.

Figure 1

(a) Lateral radiograph showing moderately displaced odontoid fracture. (b and c) T2-weighted sagittal and axial MRI scans with no evidence of TAL injury

Figure 2

Preoperative CT scan showing fracture pattern

Surgical intervention

The fracture was managed with closed reduction and halo vest immobilization [Figure 3]. Thirteen weeks later, the fracture was fused on radiographs, and the halo vest was removed [Figure 4a and b]. At 17 weeks, however, X-rays showed a slight increase in the ADI (3.18 mm) [Figure 5a]. At 5 months, the patient developed frank atlantoaxial instability [e.g., widened ADI (9.18 mm) with cervical kyphosis (C2–C6 kyphosis = 33°] [Figure 5b]. A posterior atlantoaxial C1–C2 fusion was performed utilizing sublaminar wires and iliac crest bone graft [Figure 6a]. Postoperatively, a Philadelphia collar was applied. Solid fusion was achieved at 6 postoperative months [Figure 6b], and the 2-year follow-up showed some improvement in kyphosis (41° − 12° =33°) [Figure 6c].

Figure 3

(a) Acceptable fracture reduction achieved after closed reduction in halo vest. (b) 4 weeks follow-up with well-aligned fracture

Figure 4

(a) Follow-up at 10 weeks. (b) Follow-up at 13 weeks

Figure 5

(a) At 17 weeks, slightly increased ADI (3.18 mm) with C2–C6 cervical kyphosis of 33°. (b) At 5 months, large ADI of 9.18 mm showing frank instability

Figure 6

(a) Postoperative AP and lateral radiographs after posterior fusion with sublaminar wiring and iliac crest bone graft. (b) 6 months follow-up AP and lateral radiographs showing fusion and C2–C6 cervical kyphosis of 41°. (c) 2 years follow-up showing resolution of some of kyphosis

DISCUSSION

The delayed diagnosis of a TAL associated with an odontoid fracture is rare. In a retrospective review of 77 odontoid fractures, Sayama et al. concluded that odontoid fractures do not require MRI screening for TAL injury.[7] Similarly, Debernardi et al. reported 27 cases of traumatic (type II) odontoid fractures who acutely underwent MRI (<72 h); they concluded MRI was unjustified for type II odontoid fractures.[3]

Diagnosis and treatment of C1–C2 instability

Anterior widening of ADI more than 3 mm can be seen on mid-sagittal CT reconstructed images. Perez-Orribo et al. compared the CT and MRI measurements to detect the transverse ligament injury, they concluded that no current CT-based measurements consistently indicated integrity of transverse ligament.[6] The odontoid can fail in both flexion and extension,[9] whereas TAL ligament failure results in sagittal atlantoaxial instability (e.g., anterior displacement of C1 on C2).[1]

Most odontoid fractures, except for unreducible type II lesions, can be managed nonoperatively with rigid cervical immobilization. Julian et al. reported class III evidence for the successful conservative treatment of type III odontoid fractures utilizing rigid cervical immobilization (e.g., halo vest).[5] Alternatively, odontoid fractures with concomitant TAL injuries typically require early posterior atlantoaxial fusion. Sherekar concluded that, if the lordosis of the occiput and upper cervical spine increases, the subaxial cervical spine may develop kyphosis.[8] Similarly Huang et al. reported that surgical over-reduction and hyperlordotic fusion of C1–C2 joint are associated with cervical sagittal malalignment.[4]

CONCLUSION

We recommend screening of odontoid fractures for transverse ligament injury with both MRI and CT. If conservative management is used (e.g., halo device), strict radiographic surveillance is required to look for progressive kyphosis/deformity/instability.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.